“Brake-by-wire” brake systems are becoming increasingly common in automotive engineering. A generic electrohydraulic brake system for motor vehicles of the “brake-by-wire” type is known for example from DE 102 35 288 A1, which is incorporated by reference.
In “brake-by-wire” brake systems, the brake pressure necessary in service braking is provided without the direct involvement of the vehicle driver by the pneumatic, electric or electrohydraulic actuator unit. A so-called travel simulator gives the vehicle driver the pedal feel known from conventional brake systems.
On failure of the “brake-by-wire” unit or the electrics/electronics, the vehicle is braked by hydraulic pressure which the driver generates exclusively by muscle power in the hydraulic brake master cylinder (unamplified fall-back level). Furthermore, if the brake system switches to muscle-powered fall-back level e.g. due to failure of the external energy, the travel simulator must be isolated from the pedal actuation because the volume consumer “travel simulator” would otherwise lead to a substantially extended pedal travel and can lead to inadequate vehicle deceleration. For this reason, the system itself must be able to monitor the isolation of the simulator.